Coronary vessels, partially occluded by plaque, may become totally occluded by thrombus or blood clot causing myocardial infarction, angina, and other conditions. Carotid, renal, peripheral, and other blood vessels can also be restrictive to blood flow and require treatment. A number of medical procedures have been developed to allow for the removal or displacement (dilation) of plaque or thrombus from vessel walls to open a channel to restore blood flow and minimize the risk of myocardial infarction. For example, atherectomy or thrombectomy devices can be used to remove atheroma or thrombus. In cases where infusion of drugs or aspiration of thrombus may be desired, infusion or aspiration catheters can be placed near the treatment site to infuse or aspirate. In cases where the treatment device can be reasonably expected to shed emboli, embolic protection devices can be placed near the treatment site to capture and remove emboli. In other cases, a stent is placed at the treatment site. Both embolic protection devices and stents can be placed in or near the treatment site using delivery catheters.
In percutaneous transluminal coronary angioplasty (PTCA), a guidewire and guide catheter are inserted into the femoral artery of a patient near the groin, advanced through the artery, over the aortic arch, and into a coronary artery. An inflatable balloon is then advanced into the coronary artery, across a stenosis or blockage, and the balloon inflated to dilate the blockage and open a flow channel through the partially blocked vessel region. One or more stents may also be placed across the dilated region or regions to structurally maintain the open vessel. Balloon expandable stents are crimped onto a balloon in the deflated state and delivered to the lesion site. Balloon expansion expands the stent against the lesion and arterial wall. Alternatively, self-expanding stents can be restrained in a sheath, delivered to the treatment site, and the sheath removed to allow expansion of the stent.
Embolic protection devices have been developed to prevent the downstream travel of materials such as thrombi, grumous, emboli, and plaque fragments. Devices include occlusive devices and filters. Occlusive devices, for example distal inflatable balloon devices, can totally block fluid flow through the vessel. The material trapped by the inflatable devices can remain in place until removal using a method such as aspiration. However, aspiration cannot remove large particles because they will not fit through the aspiration lumen. Also, aspiration is a weak acting force and will not remove a particle unless the tip of the aspirating catheter is very close to the particle to be removed. During the occlusion, the lack of fluid flow can be deleterious. In coronary applications, the lack of perfusing blood flow can cause angina. In carotids, seizure can result from transient blockage of blood flow. In both coronaries and carotids, it is not possible to predict who will suffer from angina or seizure due to vessel occlusion. If a procedure starts with an occlusive device, it may be necessary to remove it and start over with a filter device.
Occlusive embolic protection devices can also be placed proximal to the treatment site. Debris generated at or near the treatment site will not be transported from the treatment site if a proximal occlusive device substantially stops blood flow through the vessel. The material generated during treatment can remain in place until removal using a method such as aspiration. Generally, proximal occlusive embolic protection devices suffer from many of the same limitations as distal occlusive embolic protection devices.
Other embolic protection devices are filters. Filters can allow perfusing blood flow during the emboli capture process. The filters can advance downstream of a site to be treated and expand to increase the filter area. The filter can capture emboli, such as grumous or atheroma fragments, until the procedure is complete or the filter is occluded. When the filter reaches its capacity, the filter may then be retracted and replaced.
Embolic protection devices can be delivered over wires and within guide catheters. The embolic protection methods are normally practiced ancillary to another medical procedure, for example PTCA with stenting or atherectomy. The embolic protection procedure typically protects downstream regions from emboli resulting from practicing the therapeutic interventional procedure. In the example of PTCA, the treating physician must advance a guidewire through the aorta, over the aortic arch, and into a coronary ostium. Advancing the guidewire through tortuous vessels from a femoral artery approach can be difficult and vary with both the patient and the vessel site to be treated. Guide wires are typically selected by the treating physician, based on facts specific to the patient and therapeutic situation, and also on the training, experience, and preferences of the physician. In particular, a physician may have become very efficient in using a specific guidewire to access the left coronary ostium and then advance a balloon catheter over the positioned guidewire. The efficacy of the procedure may depend on the physician being able to use a favored guidewire.
In the example PTCA procedure, a guide catheter extends proximally from the patient's groin area, and may be about 100 centimeters long. A 320 centimeter guidewire is placed into the guide catheter and extended distal of the guide into a coronary vessel, leaving about a 200 centimeter long guidewire proximal region extending from the guide catheter. The embolic protection device delivery catheter, nominally about 130 centimeters in length, can advance over the guidewire and within the guide catheter, until a length of guidewire extends from both the guide catheter and delivery catheter. The guidewire can then be retracted and removed from the patient. In some methods, the embolic protection device then advances through and out of the positioned delivery catheter, to the target site to be protected or filtered. In other methods, delivery is accomplished by disposing the embolic protection filter device within the delivery catheter distal region, and advancing the delivery catheter and embolic protection device together within the guide catheter, optionally over the guidewire, and deploying the filter by retracting the delivery catheter while maintaining the position of the filter, thus forcing the filter distally out of the delivery catheter.
Advancement of the delivery catheter over a single length, nominally 170 centimeter long guidewire presents a problem. The treating physician can only advance the filter delivery catheter about 40 centimeters over the guidewire until the delivery catheter advances into the patient and the guidewire is inaccessible within the delivery catheter. The guidewire position should be controlled at all times so as to not be dislodged by the advancing delivery catheter from the hard acquired guidewire position within the patient.
One solution to this problem is to use a guidewire at least double the length of the delivery catheter as described above. A 320 centimeter long guidewire can extend at least about 150 centimeters from the patient's groin, having an accessible region exposed at all phases of delivery catheter placement. However, the length of the 320 centimeter guidewire makes manipulating and rotating the guidewire very difficult for the treating physician. Additional personnel can hold the extra length of the guidewire to prevent the added wire length from falling to the floor, where it would become contaminated. However, not all cardiac catheter laboratories have personnel available to maintain control of the long guidewire. In many labs, the physician is working alone in the sterile field. Advancing a device delivery catheter over a positioned, favored, and short (175 centimeter) guidewire would be inherently more efficacious than requiring use of an unfamiliar, disfavored, or double length guidewire to position the delivery catheter.
Another alternative catheter design is the monorail or rapid exchange type such as that disclosed in U.S. Pat. No. 4,762,129, issued Aug. 9, 1988, to Bonzel. This catheter design utilizes a conventional inflation lumen plus a relatively short parallel guiding or through lumen located at its distal end and passing through the dilatation balloon. Guide wires used with PTCA balloon catheters are typically 175 centimeters in length and are much easier to keep within the sterile operating field than 300 to 340 centimeter guidewires. This design enables the short externally accessible rapid exchange guidewire lumen to be threaded over the proximal end of a pre-positioned guidewire without the need for long guidewires.
Still needed in the art are improved designs for rapid exchange delivery catheters. Such delivery catheters can be used to deliver various treatment and/or diagnostic devices including embolic protection devices.
It is desirable to place a distal protection device at a chosen location in order to achieve good sealing between the device and the wall of the vessel. Frequently it is necessary to match the protection device diameter with the vessel diameter, and vessels are known to taper or to have diameters that vary due to disease. It is also desirable to place the protection device in a relatively disease free portion of the vessel so as to minimize liberation of emboli from the wall of the vessel due to interaction with the protection device. Further, it is desirable that the device remains at the desired location during the procedure. Excessive motion of the wire or elongate guide member used to deliver the device can advance a protection device distally, beyond branch vessels, which thereby become unprotected from emboli.
Distal protection devices typically are mounted on a wire or tube that functions as a guidewire. As used herein the term guidewire means either a traditional guidewire or other elongate member or hollow tube that is used in delivering the distal protection device. The protection device can be either a filter or an occlusive device such as a balloon. The distal protection devices are either fixedly attached to the guidewire or attached so as to permit a limited amount of motion between the device and the guidewire. Frequently, the same guidewire used to carry the device is also used to guide various catheters to and from the treatment site. For example, during the procedure, catheters may be exchanged over this guidewire. When catheters are exchanged inadvertent wire movement can cause the protection device to move within the vessel. Excessive wire motion can also retract a protection device proximally, where it can potentially become entangled in a stent or even be inadvertently removed from the vessel being protected. In some vessels, when guide catheters are repositioned, the protection device also tends to move within the vessel. This is undesirable because captured emboli can be released and/or new emboli can be formed distal to the protection device, blood vessels can be damaged, and/or the device can entangle with an implant such as a stent. Therefore, it is clear that too much movement of the device within the vessel could have catastrophic results.
Some work already has been done to provide for limiting the movement of a distal protection device or distal filter with respect to a guidewire. For example, a guidewire having a distal stop is described in WO 01/35857 (Tsugita et al.). The filter slides on the guidewire but cannot slide off the wire due to the distal stop. Another device which includes a slideable vascular filter having both distal and proximal sliding elements that move independently of each other over a mandrel is described in WO 01/21100 (Kusleika et al.). While this system meets many of the needs in the art, it limits the range of motion of the filtration device on the guidewire, and the precision with which it can be placed is limited. Still further embodiments of devices which allow increased independence of movement of the guidewire without moving the embolic protection device are disclosed in U.S. Pat. No. 6,773,448 B2, issued Aug. 10, 2004, to Kusleika et al.
Another known limitation of distal protection devices relates to wire bias. It is well known that a guidewire will conform to the outside of a curved vessel on advancement of the wire in a distal direction and will conform to the interior of a curved vessel during retraction of the wire. Most distal protection devices are attached to wires, and when they are deployed in vessel curvature the wire bias will alternately move the device between the inside and the outside of the vessel curve. For filters this can defeat the protection effect by compressing the filter opening. For occlusion devices the wire bias effect can cause excessive motion of the occlusion device with potential liberation of embolic debris from the vicinity of the occlusive element.
Some work already has been done to provide for limiting the radial movement of a guidewire relative to a distal protection device. For example, a protection device having a proximal loop is described in U.S. Pat. No. 6,740,061 B1, issued May 25, 2004, to Oslund et al.), the contents of which are incorporated herein by reference. A loop is provided proximal to the filter to immobilize the wire against the vessel wall regardless of wire bias. While this system meets many of the needs in the art, it adds bulk to the device and thereby limits crossing profile.
It would be desirable to have a distal protection system that can be precisely placed at a location within the vasculature and that can accommodate some range of axial and/or radial wire motion without disturbing the device's position. Further, when the embolic protection device is a filter it would be desirable that the host wire which carries the filter be centered within the lumen when the device is deployed.